In the manufacture of paper, plastic film or the like, web breakage occasionally occurs. Web breakage presents the operator with the difficult problem of rethreading the web, especially when the break occurs on continuously running machines, such as papermaking machines, since it is undesirable to shut down the machines completely due to attendant startup difficulties, etc. As a consequence, it is a commonly used technique for the machine operator and his assistants to attempt to manually grasp the free end or tail of the web on the fly while the machine continues to operate and direct it into close proximity with the next station, such as a roll nip. It will be appreciated that this is a difficult and dangerous procedure and it is possible for a person attempting to rethread a machine in such manner to become injured, even to the extent of losing fingers or hands. Also, this standard procedure is often quite time-consuming with numerous attempts to thread the web tail often being necessary before success is attained. Until rethread is successfully accomplished, production is lost.
With particular reference to paper machines, film rewinders and the like, various air jet arrangements have been employed in an attempt to blow the tail of the web into the next work station. An example of such an air jet arrangement is given in U.S. Pat. No. 3,066,882, C. B. Havens et al., issued Dec. 4, 1962. The problem with conventional air jet blower arrangements has been that they can be used only to deflect or convey the web tail end over relatively short distances. This is true even when conventional air jets are used in conjunction with a chute or other guide for the web tail or when a number of air jets are spaced along the web path. Further, such arrangements are inefficient since they use relatively large quantities of pressurized air. Over relatively large distances, 5-20 feet or even longer, the only feasible approach to rethreading a web tail "on the fly" has been the manual "bucket brigade" type of operation with all its attendant safety problems. It might be pointed out that in papermaking machines, for example, such long distances between the operation stages of the machine are not at all uncommon. The inability of prior art approaches to convey web tails over relatively long distances during the rethreading operation occasionally means that the machines running the webs cannot be run at their full operational capabilities. For example, it is not unknown for paper machines or the like to be run at slower speeds than they are capable of because of fear of web break and the heretofore time-consuming process of rethreading that would then be required. This is especially true where web break could possibly occur at a difficult rethreading location such as at a calender stack. Apparatus constructed in accordance with the teachings of the present invention can be used to rethread webs promptly and efficiently in even difficult locations such as at calender stacks. Hence, fear of web breakage occurring occasionally will not act as a deterrent to the efficient operation of the machine when the present invention is being utilized in conjunction therewith.
The present invention provides a system of relatively inexpensive and simple construction which utilizes a phenomenon known as the "Coanda effect" to entrain the free end or tail of a moving web of flexible material and direct it to a desired location such as the nip formed between two relatively movable rolls. The Coanda effect itself has been known for many years, as exemplified by U.S. Pat. No. 2,052,869, issued to Henri Coanda. Briefly, this phenomenon can be described as the tendency of a fluid, which emerges from a slit or similar restricted opening under pressure, to attach itself or cling to and follow a surface in the form of an extended lip of the slit, which lip recedes from the flow axis of the fluid as it emerges from the slit. This creates a zone of reduced pressure in the area of the slit so that relatively large quantities of ambient air or other entrainable material which are in the zone will become entrained and flow with the fluid which has attached itself to the extended lip.